1. Field of the Invention
This invention relates to apparatus for transmitting directional light beams, and more particularly, to apparatus for transmitting a light beam in any desired horizontal direction.
2. Description of the Prior Art
A very precise aim of a light beam toward the location of a receiving station is needed for a communication system operating with the optical transmission of signals, especially where a laser beam of coherent light in the visible or in the infrared range is utilized. When a signal must be sent in response to a query signal, an exact determination of the direction from which the query signal was sent is necessary, and an appropriate transmission of the reply message must be made in this same direction. For many operations, in which response signals must contact several querying stations in rapid succession, or must reach a station which is moving rapidly from place to place, the directional tuning or tracking of the transmitter to the specific point of origin of each received signal must be accomplished within an extremely short time after receipt of the signal.
In hitherto available variable light transmitters, which direct a light ray at any desired azimuth angle with respect to a vertical axis, a light ray emitting element is utilized which may be rotated around the vertical axis. This element may be either the light source itself, such as a laser, or a reflector, prism, or similar optical element, which deflects the direction of the light beam. Thus, if the direction of transmission must be changed by an angle .phi., the emission element must be rotated by the same angle .phi. about the vertical axis. When the direction of transmission changes rapidly, rotations of the beam in rapid succession, with angular deviations as large as 180.degree., must be made. Consequently, previously available variable light transmitters have required relatively long tuning and tracking times, which, in addition, are not constant, but vary directly as a function of the angle differential between the former directional setting and the required directional setting.
Therefore, it is a feature of this invention to provide an optical transmitter which will tune and track received optical signals with very little time loss and with a high degree of accuracy.
It is also a feature of this invention to provide an optical transmitter in which no rotation of the light emitting element around a vertical axis is necessary to aim the light ray at a desired azimuth angle.
It is another feature of this invention to provide an optical transmitter in which the projection of a light beam at a desired azimuth angle is achieved by very small position shifts or tilts of the light emitting element, thereby presenting a very exact and low inertia tracking device.
A further feature of this invention is to provide an optical transmitter and receiver permitting unidirectional reception and return signaling.
It is yet another feature of this invention to provide an optical transmitter which permits the projection of an emitted light ray in a uniform direction to all sides.
It is also a feature of this invention to provide an optical transmitter and receiver which is especially suited for communications lines between vehicles, ships, and the like, and is suitable for military uses, such as the simulation of artillery practice or manuevers, or contact between mobile military units, and as well for civilian purposes, such as, for example, in construction, oil fields, or contact between fishing boats.
It is in addition another feature of this invention to provide an optical transmitter and receiver which may transmit and receive omnidirectionally or monodirectionally, which will detect the angle of an incident light beam, and which may be used to establish laser communication lines by manual or automatic selection, either omnidirectionally or monodirectionally.